In Windows Explorer search for *.pst.
If such a file is found (which it ought to be) and it is 2GB size, then that's your problem.
Another possibility is that yoou've got one or more add-ins associated with Outlook and one of them was actively working when you thought you had closed Outlook and then switched off the PC. That would corrupt the PST file.
Suspishio
My advice is at your risk
Qosmio G50-10H; T9400 2.53GHz Core 2 Duo; 4GB RAM; Vista HP (32)
nForce 680i LT; Q6600 Quad Core 2.4GHz; 8GB RAM; XP Pro (64)
Dell XPS M1710; T7200 2GHz Core 2 Duo; 2GB RAM; XP Pro (32)